THE T-BOX GENE FAMILY

A novel family of transcription factors that appears to play a critica l role in the development of all animal species was recently uncovered on the basis of homology to the DNA binding domain of the Brachyury, or T locus, gene product. Phylogenetic studies have shown the ancient origin of this gene family, which has been named the T-box family, pri or to the divergence of metazoa from a common ancestral type. T-box ge nes have now been identified in the genomes of C. elegans, Drosophila, sea urchin, ascidian, amphioxus, Xenopus, chick, zebrafish, mouse, an d human and will probably be found in the genomes of all animals. Alth ough functional analyses of T-box family members have just begun, the results show a wide range of roles in developmental processes that ext end over time from the unfertilized egg through organogenesis. Only a few mutations in T-box genes are known, but all have drastic effects o n development, including a targeted mutation in mice causing an embryo nic lethal phenotype, and two human T-box gene mutations that results in developmental syndromes. This review presents a current overview of progress made in the analysis of T-box genes and their products in a variety of model systems. (C) 1998 John Wiley & Sons, Inc.